1. Field of the Invention
The present invention generally relates to variable inductor devices and, more particularly, to variable inductor devices used in mobile communication units.
2. Description of the Related Art
In electronic equipment which must be miniaturized and more particularly in mobile communication units such as mobile cellular telephones and automobile telephones, there is a demand for reducing the size of components used therein. As the frequency in a mobile communication unit is increasing, the circuitry is becoming more complicated, and thus, only a small deviation is allowed for the components used in the unit.
In order to obtain a circuit having a tap center connected to the electrical midpoint of a coil, the following configuration is conventionally used, as illustrated in FIG. 25. Two coil components 201 and 202 are mounted on a printed circuit board 206 and are electrically connected to each other via circuit patterns 203 and 204 and a tap center pattern 205 is provided on the printed circuit board 206. Further, the following methods have been proposed to vary the inductances of the coil components 201 and 202 while keeping the inductances in balance with each other. The coil components 201 and 202 are simply replaced with alternative coil components having different and properly balanced inductances. Alternatively, variable coils are used as the coil components 201 and 202 to gradually and suitably vary the inductances of the coils.
In the above methods, however, the inductances of the two coil components 201 and 202 cannot be properly balanced because of variations in the inductances of the coil components 201 and 202 and a positional displacement in mounting the coil components 201 and 202. This may sometimes cause the tap center pattern 205 to be connected to a portion deviating from the electrical midpoint of the coil which is formed by the coil components 201 and 202. Further, as noted above, the coil components 201 and 202 are electrically connected to each other via the tap center pattern 205 disposed on the printed circuit board 206, thereby requiring that an overall area printed circuit board 206 be very large.
Moreover, according to the first conventional method for varying the inductances by replacing the coil components 201 and 202 with alternative coil components, the removing operation of the coil components 201 and 202 is very complicated, thereby making it hard to automate the required operation. On the other hand, according to the second conventional method for varying the inductances of the variable coils while keeping them in balance with each other, the adjusting operation is very complicated and troublesome. Because of this reason, it is difficult to automate the required operation.